LCDs that lead the display industry at present and OLEDs (organic light emitting diode) that rise as a popular display device of next generation have established techniques of using a conventional glass as a substrate material and forming transparent electrodes thereon. However, in recent years, active researches have been conducted for realizing so called a flexible display which uses a polymer film as a substrate.
However, when using electrode materials such as the conventional ITOs used for forming transparent electrodes on a glass substrate, the electrode formation is performed through a heat treatment at a high temperature of at least 180° C., and preferably 200° C. or higher for several minutes to 20 to 30 minutes. Thus, it is necessary to develop a polymeric material that has both colorless transparency and heat resistance as a flexible substrate material.
Meanwhile, an aromatic polyamide compound has high strength, high elasticity, high heat resistance, insulating properties, and low moisture and gas permeability. Thus, it is used as a material in the electric and electronic field such as a high performance magnetic tape for storing digital data or a flexible print circuit substrate.
However, mostly known para-substituted aromatic polyamides have very low solubility in a solvent. Thus, in order to dissolve the compound in a polar organic solvent, a fair amount of inorganic substance (LiCl or CaCl2) is added. This inorganic substance must be removed from the film in a subsequent wet process, thus the processing process becomes complicated.
Moreover, a yellow or brown coloration may occur by the electron transfer between a benzene core and an amide group. Therefore, such a film does not satisfy the requirements as an optical material in the field of an optical communication, a display, or the like.
Moreover, there have been patents and researches reported in relation to polyimide-based aromatic polyimide films and the production methods thereof having a low coloration (YI of about 7) and high transparency.
However, these films are expensive or the coloration problem has not been solved sufficiently. Thus, they have not reached the point of commercialization.